1
2
1-Feb
4
✅ The correct answer is option B.
Heat Transfer MCQs
42. The inner wall of a furnace is at a temperature of 700°C. The composite wall is made of two substances, 10 and 20 cm thick with thermal conductivities of 0.05 and 0.1 W.m-1.°C-1 respectively. The ambient air is at 30°C and the heat transfer co-efficient between the outer surface of wall and air is 20 W.m⁻².°C-1. The rate of heat loss from the outer surface in W.m-2is
165.4
167.5
172.5
175
✅ The correct answer is option A.
43. Multiple effect evaporators ar used to
Increase the steam economy & decrease the capacity
Increase the steam economy & the capacity
Decrease the steam economy & the capacity
Decrease the steam economy & increase the capacity
✅ The correct answer is option B.
44. When the ratio of the Grashoff number and to the square of Reynolds number is one, the dominant mechanism of heat transfer is
Free convection
Entry length problem in laminar forced conduction (developing thermal boundary layer)
Mixed convection (both free and forced)
Forced convection
✅ The correct answer is option C.
45. Heat transfer co-efficient equation for forced convection, Nu = 0.023 Re0.8 . Prn, is not valid, if the value of
N = 0.4 is used for heating
N = 0.3 is used for cooling
Reynolds number for the flow involved is > 10000
Reynolds number for the flow involved is < 2100
✅ The correct answer is option D.
46. The type of liquor circulation system to be ‘ employed in evaporators (viz. natural or forced circulation) is determined mainly by the __________ of the liquid.
Viscosity
Density
Thermal conductivity
Corrosive nature
✅ The correct answer is option A.
47. When vaporisation takes place through a blanketting film of gas, the phenomenon is termed as __________ boiling.
Pool
Nucleate
Transition
Film
✅ The correct answer is option D.
48. Evaporation of 1kg of water from a solution in a single effect evaporator requires about __________ kg of steam.
0.4 – 0.6
1-1.3
1.8-2
2 – 2.4
✅ The correct answer is option B.
49. Tube pitch is the __________ of tube diameters and the clearances.
Sum
Difference
Ratio
None of these
✅ The correct answer is option A.
50. The equivalent diameter for the annulus of a double pipe heat exchanger, whose inner pipe has fins on the outside is __________ compared to the same size pipes without fins.
More
Less
Same
Unpredictable
✅ The correct answer is option B.